The present invention relates to the art of chewing gums and, in particular, to a novel chewing gum base composition in which the resin and elastomeric components of the base are compatibilized by a single polymeric compatibilizing agent.
Chewing gums generally contain two distinct constituent parts, a water-soluble portion which is dissipated in the oral cavity during chewing and a base portion which is inert and essentially insoluble in water and is retained in the mouth throughout mastication.
The present invention is concerned with the base portion of the gum and the materials of which it is composed. These materials are critical in effecting the properties and characteristics of the chewing gum which are determined by the intended utility of the gum.
Presently, chewing gum bases are made of two primary components which have been considered essential in producing the desired gum base characteristics, a resinous material and an elastomeric material, either of which may be of natural or synthetic origin or even combinations of both.
The elastomer component generally provides an insoluble bulking constituency with resiliency to recover from deformation caused by chewing.
The resinous base component is determinative of other characteristics and usually must satisfy more than one requirement. Primarily the resinous component must impart a permanent chewability to the gum base, i.e., resistance to the stiffening and poor taste which is usually evident upon continued mastication of a chewing gum product. Further, the resin must be non-toxic, odorless, tasteless, hydratable, somewhat elastic, economical, insoluble in water, resistant to decomposition and embrittlement upon aging, capable of maintaining flavor and resistant to formation of toxic products.
Although synthetic resins, such as polyvinyl acetate, which impart many improvements to the chewing gum, have currently replaced chicle and other natural resins which were utilized in the past, these synthetic resins are nevertheless generally characterized by a need to have their plasticity and chewing properties improved. Furthermore, combining the elastomer component with a resinous material has proven somewhat difficult in that these components exhibit little if any, miscibility, solubility and/or compatibility with one another. Overcoming this problem has been shown to be essential in the preparation of a stable homogeneous gum base. This problem is compounded by the addition of other components which are required to effect different desired characteristics to the resulting chewing gum. Addition of these other components while maintaining proper resiliency throughout mixing is also known to be problematic, but necessary in order to achieve a desired homogenous insoluble phase of the chewing gum.
Both elastomers and polymeric resins inherently have a characteristic intensity of intermolecular interaction called cohesive-energy density, which, in general, must be overcome to some extent to achieve compatibility between these two components. Attractive forces between organic molecules which account for the characteristic cohesive-energy density include among other forces, Van der Waals forces, dispersion forces, dipole induced dipole forces, and acid base forces, of which the most important is hydrogen bonding. Authorities have referred to various criteria for compatibility, i.e., clarity, heat capacity (merging of separate glass transition, Tg, peaks or melting points), X-ray scattering, thermal expansion vs. temperature and dielectric or mechanical measurements. However, many of these criteria are not altogether reliable. Indeed, while much of the early literature is too subjective, more recent references may be considered overly vigorous.
Thus, while predicting blend compatibility has not been reduced to an exact science, solubility parameter methods have been found useful because there is significant data available. A Hildebrand solubility parameter, .delta., is an expression of the cohesive energy density of a particular substance which is defined as the square root of the energy of vaporization per unit volume of material. Thus, the solubility parameter is proportional to the cohesion of the material or the strength of attraction between the molecules making up the material. In theory, the miscibility of polymers relates to those having comparable solubility parameters. In the case of low molecular weight substances, one would expect miscibility if the solubility numbers are within 5-9 units of each other. Polymeric substances are more difficult. For example, a solubility parameter member difference of 0.5 may be too much at 5,000 MW for both polymers or ever 0.15 difference may be too much of a difference at 50,000 MW. Generally, however, compatibility is considered possible between those polymers having a difference in solubility parameters of less than 1.7 to 2.0, S. Krause, "Polymer Capability," J. Macromal. Sci-Macromal Chem C7, pgs. 251-314 (1972).
While it is known that straight mechanical shearing may be used to intimately contact polymers having disparate chemical and structural properties, such methods may also depolymerize the components thus destroying desired inherent polymeric properties such as memory, elasticity, and film-forming capabilities, i.e., relative displacement without rupture of intermolecular bonding. To overcome these problems different ingredients have been used in an attempt to compatibilize resins and elastomers externally without total depolymerization while maintaining all the properties for which the other ingredients have been intended.
In particular, certain plasticizers have been employed to effect proper external plasticization of each primary components of the gum base, i.e., the resin material and the elastomer component, and to increase the solubility, miscibility, and compatibility of these two components during preparation, production, and chewing. In order to eliminate the need for individual compatibilizers for each of the primary components, it has been the goal of work in the gum base art to use a single external compatibilizer to achieve an adequately plasticized gum base formed from an elastomer and a resin.
It is therefore an object of the present invention to provide a single compatibilizing agent which is capable of properly plasticizing both the resinous and the elastomeric components of a gum base.
It is another object of the present invention to provide a homogeneous polyblend gum base containing a single compatibilizing agent which resists migration from the base.
It is still another object of this invention to provide a chewing gum containing the aforementioned homogeneous polyblend gum base.
A still further object of this invention is provide a process for the preparation of a chewing gum containing the aforementioned homogeneous polyblend gum base.